Evidence has been obtained indicating that: (1) During the angiogenesis process, copper ions are concentrated in the corneal tissue before invasion by new formed capillaries; (2) Animals in copper deficient diet are unable to form new capillaries in the corneal test; (3) Prostaglandin E1 is able to induce angiogenesis and to concentrate copper ions in the corneal tissue before new formed vessels appear; (4) Indomethacin-treated animals are unable to form new capillaries in the corneal test. Both copper and PGE appear to be indispensable components of the angiogenesis process.